The present invention relates to method and apparatus for treatment of industrial waste water and particularly to methods and apparatus for safe effective removal of chromium compounds from effluent from chrome plating processes. The Chromic acid which is normally encountered in plating processes is considered toxic and since it is removed from the plated parts in a rinse station the rinse water must be treated prior to introduction to sewage systems.
In most cases the prior art has provided for such chromic acid bearing rinse water to be treated with chemical reducing agents followed by treatment with alkaline material to form a solid precipitate which can then be more easily handled for disposal and allows the water to be discharged to sewage systems or otherwise disposed of.
Typically, the removal is controlled by the oxidation-reduction potential of the system. In the first step, the pH of the rinse water is lowered to a selected range by introduction of an acid followed by reduction by a sulfite and hydroxide to increase the pH to precipitate the chromium as a hydroxide salt. Such procedures have required at least three vessels, two pH meters, and a oxidation-reduction potential monitor.
Such prior art methods and apparatus are labor intensive because of the multiple steps required and expensive because of the equipment and chemicals required. Further, the prior art methods are at best only marginally effective and the multiple step operation is subject to error and inadvertent emission of toxic material.
Moreover the prior art methods are not capable of conversion to effective procedures for continuous processing of rinse water and return of the water to the process so there is no liquid discharge from the process.
My U.S. Pat. No. 5,256,306 teaches treatment of such rinse water with hydrazine and a cobalt catalyst for safe removal of the chromic acid. The present invention is an improvement on the teaching of my prior Patent.
No prior art method is known which allows continuous treatment of rinse water from a chrome plating process with no liquid discharge from the rinse water treating apparatus.